In conventional seat belt devices such as the three point seat belt devices which are used in vehicles, a shoulder anchor device is used in order to make it possible for the seat belt to fit passengers of different bodily builds, who assume different postures while driving. The shoulder anchor device makes it possible to adjust the support or attachment position where the shoulder belt for restraining the upper body is attached to the vehicle on the shoulder side. Normally the support or attachment position is adjusted vertically, so that the support position of the shoulder belt is prevented from being moved or shifted in, for example, a vehicle collision.
In FIGS. 1 to 3 which show this kind of conventional anchor device, an adjustment base 1 is fixed to, for example, a center pillar of the vehicle body (not shown) in its longitudinal direction (up-down direction of the vehicle body). An adjustable anchor 2 is attached to the adjustment base 1 so that is can move in the vehicle's up-down direction. The adjustable anchor or runner 2 cannot move in the longitudinal direction of the adjustment base or guiding member 1 when the lock pin 3 is mated with one of the engaging openings 6 which are provided at specified intervals in that direction; when the pin is pulled out from the hole, it can move. Fixed to the adjustable anchor 2 through some means such as coupling is a through-anchor 4 through which a shoulder belt 5 passes.
It is known that the input load applied to the shoulder belt 5 can reach as much as two tons during a vehicle collision. For this reason, in order to insure that the shoulder belt will be strong enough to perform reliably in such an emergency, the anchor device must be sufficiently strong in the input transmission path to the vehicle side. This is one of the most important design requirements.
Now, the construction of conventional anchor devices, particularly the adjustable anchor 2 is explained with reference to the transmission of the shock force.
A shock is input from the shoulder belt 5 through the through-anchor 4 in the X or X' direction in FIG. 1, transmitted to the adjustable anchor 2, and then through the lock pin 3 to the adjustment base 1. Consequently, since an anchor bolt 8 is used in order that the adjustable anchor 2 is securely coupled to the through-anchor 4 through which the shoulder belt 5 passes, it is necessary for the attachment strength of the anchor bolt 8 to be maintained sufficiently strong to resist the shock. The strength of the attachment of the lock pin 3 to the adjustable anchor 2 also must be adequate in order for the load to be transmitted to the adjustment base 1 without difficulty.
In addition, the construction or strength of the adjustable anchor 2 must be focused. Supposing that the adjustable anchor 2 becomes deformed, the lock pin 3 will be displaced relative to the adjustment base 1 and the pin will be released from its coupling to the adjustment base 1, resulting in that the effectiveness of restraint of the passenger is greatly reduced or lost in the adjustable anchor device. Therefore, it is important for both the strength of the adjustable anchor 2 itself and the coupling of the lock pin 3 to the adjustable anchor 2 to be adequate.
In order to meet these requirements, and make it easy to adjust the position of the adjustable anchor 2, the adjustable anchor 2 in an improvement has opposing arms 2a and 2b on its rear side to form a square C shape in cross section which can maintain a cross-sectional area enough to keep the attachment strength, as shown in FIG. 3. Using this shape, the through anchor 4 is fastened by the anchor bolt 8, and the design permits the lock pin 3 to be supported by the upper and lower side portions of the C-shaped adjustable anchor 2. Then by moving the lock pin 3 from the upper side portion to the lower one or form the lower side portion to the upper one, the lock pin 3 becomes coupled to or decoupled from the engaging opening 6 of the adjustment base 1. Accordingly, the C-shaped adjustable anchor 2 can move along the adjustment base 1, in the vertical or up-down direction relative to the vehicle, with its inner surfaces sliding on the adjustment base 1. Thus the movement of the C-shaped adjustable anchor 2 can be made only when the lock pin 3 is decoupled from the adjustment base 1.
However, when the space inside the vehicle cabin is limited, it can become impossible for the adjustable anchor 2 to have the necessary cross-sectional area. Accordingly, some measures must be taken to compensate for; for example, increasing the plate thickness of the adjustable anchor 2, using stronger material for the adjustable anchor 2, using induction hardening to increase the surface hardness of the section of the adjustable anchor 2 to which the lock pin 3 is coupled, or forming the adjustable anchor 2 in a closed square shape. All of these measures increase weight and/or cost.
The purpose of this invention is to solve these problems and to provide a more highly reliable adjustable anchor device without sacrificing vehicle space.